HashMap Vs LinkedHashMap in Java

Last Updated: 22 January, 2023

HashMap and LinkedHashMap are available in the java.util package, both of which implement the Map Interface and accept the data in the form of key-value pairs. Both have almost the same behaviour because LinkedHashMap is a child class of HashMap.

There are many differences between the HashMap and TreeMap that are given below.

👉 HashMap

The HashMap class was introduced in the Java 1.2 version and is available in the java.util package. HashMap is a child class of the AbstractMap class, and it implements the Map interface as well as the Cloneable and Serializable interfaces.

HashMap is used to store the data in the form of key-value pairs, where keys must be unique and values may be duplicated. HashMap accepts only one null key and multiple null values.

Java HashMap Class Declaration

public class HashMap<K,V> extends AbstractMap<K,V> implements Map<K,V>, Cloneable, Serializable

Here, K is the key Object type and V is the value Object type.

Java HashMap important features:

By default, HashMap is a non-synchronized class.
HashMap uses the hash table concept to store the data.
HashMap does not maintain data insertion order.
HashMap's initial capacity is 16, and the load factor is 0.75.
If the application demands faster insertion and retrieval, then HashMap is the ultimate choice.

👉 LinkedHashMap

The LinkedHashMap class is a child class of HashMap. It was introduced in the Java 1.4 version and is available in the java.util package.

A LinkedHashMap is used to store the data in the form of key-value pairs. The implementation of LinkedHashMap is based on hash table and linked list.

LinkedHashMap maintains the insertion order of data.

Java LinkedHashMap Class Declaration

public class LinkedHashMap<K,V> extends HashMap<K,V> implements Map<K,V>

Here, K is the key Object type and V is the value Object type.

Java LinkedHashMap important features:

LinkedHashMap does not allow duplicate keys, but values may be duplicate.
LinkedHashMap allows only one null key and multiple null values.
LinkedHashMap is a non-synchronized class by default.
LinkedHashMap uses the hash table concept to store the data.
LinkedHashMap's initial capacity is 16, and its load factor is 0.75.

👉 HashMap and LinkedHashMap have the following differences:

HashMap	LinkedHashMap
HashMap extends the AbstractMap class.	LinkedHashMap extends the HashMap class.
HashMap does not maintain the insertion order of elements.	The insertion order of elements is preserved by LinkedHashMap. (Major Difference)
HashMap uses hash tables to store maps.	LinkedHashMap uses a hash table along with a linked list to store maps.
HashMap was introduced in the JDK 1.2 version.	LinkedHashMap was introduced in the JDK 1.4 version.
HashMap required less memory than LinkedHashMap.	LinkedHashMap required more memory than LinkedHashMap.
HashMap gives faster performance than LinkedHashMap.	LinkedHashMap's performance is a bit slower than HashMap's.

👉 Example of HashMap and TreeMap in Java

Example 1: A sample Java program of HashMap

  
  import java.util.HashMap;
  import java.util.Map;
  public class HashMapExample {
    public static void main(String[] args) {
      // Creating HashMap
      HashMap<String, String> map = new HashMap<>();
        
      // Inserting data in the form of key-value pair using put() method
      map.put("in", "India");
      map.put("us", "United State");
      map.put("en", "England");
      map.put("ca", "Canada");
  
      System.out.println("Iterating Hashmap and printing Key and Value");
      for (Map.Entry m : map.entrySet()) {
        System.out.println(m.getKey() + " - " + m.getValue());
      }
    }
  }

Output

Iterating Hashmap and printing Key and Value
in - India
en - England
us - United State
ca - Canada

Example 2: A sample Java program of LinkedHashMap

  
  import java.util.LinkedHashMap;
  import java.util.Map;
  public class LinkedHashMapExample {
    public static void main(String[] args) {
      // Creating LinkedHashMap
      LinkedHashMap<String, String> map = new LinkedHashMap<>();
      
      // Inserting data in the form of key-value pair using put() method
      map.put("in", "India");
      map.put("us", "United State");
      map.put("en", "England");
      map.put("ca", "Canada");
      
      System.out.println("Iterating LinkedHashMap and printing Key and Value");
      for (Map.Entry m : map.entrySet()) {
        System.out.println(m.getKey() + " - " + m.getValue());
      }
    }
  }

Output

Iterating LinkedHashMap and printing Key and Value
in - India
us - United State
en - England
ca - Canada

That's all guys, hope this Java article is helpful for you.

Happy Learning... 😀

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